One of the most consistently documented characteristics of children with specific language impairment (SLI) is difficulty in the acquisition of grammatical morphology. Current theories of SLI center of this deficit area; however, complete evaluation of available theories is difficult because data exist which are both consistent and inconsistent with current accounts. In order to fully evaluate available positions, and to construct more complete accounts, SLI children's performance on a wider range of linguistic skills must be appraised. The area of derivational morphology appears ideally suited to this challenge. Thus, the general aims of this proposal are to assess the acquisition of derivational morphology in children with SLI, to determine whether the acquisition of derivational forms is particularly challenging for children with SLI, and to apply the resulting developmental patterns to the evaluation of current accounts of the disorder. Two studies will be conducted. The first study involves a cross-sectional examination of the use of six derivational morphemes by SLI children and two typically developing groups, one equated to the SLI subjects on the basis age, and the other on the basis of language ability. The target derivational morphemes will be elicited via picture tasks involving real- and nonce-word items. Analysis of variance procedures will be used to analyze these data. The extent to which derivational morphemes are problematic for children with SLI relative to their age- and language- mates will be considered, and results will be interpreted in light of major accounts of SLI children's morphological deficits. In the second study, the development of derivational morphology in five of the SLI subjects from the first study will be tracked longitudinaily for a two- year period. Again, patterns of derivational form acquisition will be evaluated relative to current theoretical accounts of SLI.